An exhaust system according to the preamble of claim 1 is known from DE 10 2006 049 591 A1. Urea or a urea/water solution is fed as a reactant into the exhaust gas flowing in an exhaust gas-carrying pipe in this prior-art exhaust system. A selective catalytic reduction, during which nitrogen oxides are reacted into nitrogen, takes place with the urea/water mixture mixed with the exhaust gas in the area of a catalytic converter device provided in the exhaust system or in the exhaust gas-carrying pipe.
To improve the mixing of the urea/water mixture with the exhaust gas, the urea/water mixture is brought into a superheated state prior to being released into the exhaust gas in this prior-art exhaust system. This prior-art exhaust system has for this purpose a heating unit with an electrically operable heater, which raises the temperature of the urea/water mixture to a superheated temperature. To prevent the urea/water mixture from evaporation already before its release into the exhaust gas, the pressure of this mixture is raised by a pump delivering the urea/water mixture to a pressure above the vapor pressure prevailing in association with the superheated temperature. When releasing the initially superheated urea/water mixture, which is maintained in a liquid state, into the exhaust gas, this urea/water mixture decompresses spontaneously, so that this mixture with partially evaporate, on the one hand, and very fine liquid particles will be generated, on the other hand, and very good mixing of the reactant mixed with the exhaust gas is achieved.